Electric vehicles are becoming more and more prevalent. These vehicles include hybrid vehicles, such as extended range electric vehicles (EREV) that combine a battery and a main power source, such as an internal combustion engine, fuel cell system, etc. EREVs typically employ a high voltage battery and a low voltage battery. The high voltage batteries can be various battery types, such as lithium-ion, nickel metal hydride, lead acid, etc. EREV's low voltage batteries are usually flooded lead acid (FLA) batteries, and usually provide 12.6-15.0 volts for use by on-board computers, entertainment systems, navigation systems, lighting, etc., in a vehicle. An important function of the low voltage battery is to close the contactors of the high voltage bus, which ensures operation of a hybrid vehicle. In other words, if the low voltage battery is depleted, the vehicle will not run.
A user expectation of a plugin hybrid vehicle is the ability to plug it in, leave it for some time unattended, and to be able to return later and simply drive off. However, during the time when a vehicle is parked, the low voltage battery provides power to electronic modules to allow them to maintain information (aka memory) and perform other vital vehicle monitoring functions. This key off load can deplete the 12 Volt battery over time. In addition, many vehicles have cellular links to a user's smart phones, which are powered by the low voltage battery that can allow the user to request the status of the vehicle. These loads may deplete the low voltage battery to a point where it will not be able to close the contactors of the high voltage battery.